Persons who work in contaminated environments commonly wear respirators to protect themselves from inhaling contaminants that are suspended in the surrounding air. The respirators—also referred to as “filtering face masks”—may have a filter element integral to the mask body (see, for example, U.S. Pat. No. 5,307,796 to Kronzer et al.) or separately attachable (see, for example, U.S. Pat. No. 5,579,761 to Yuschak et al.). In either instance, the respirator must comfortably provide the wearer with protection from airborne particles or unpleasant or noxious gases over the useful service life of the filter element. To achieve this goal, the filter element needs to remove the contaminants without early clogging and with minimal effort or energy requirements. Because the wearer commonly supplies the energy needed to draw air through the filter media, less resistance to airflow means that the wearer does not need to work as hard to breathe clean air—hence, a more comfortable mask. This resistance of air-movement through the filter media is commonly referred to as “pressure drop”. Lower pressure drops are desired across filters because they allow air to be filtered with greater ease. Wearer comfort is important in respirator design because uncomfortable masks are more likely to be removed from a wearer's face in a contaminated environment. In addition to providing lower pressure drops, the respirator also should fit comfortably on the face without stress to the neck and without obstructing the wearer's field of view.
To achieve appropriate levels of filter performance—such as those defined in 30 C.F.R 11 subpart K §§11.130-11.140-12 (1987), 42C.F.R Part 84 (July 1995), DIN 3181 Part 2, “Atemfilter für Atemschultzgeräte” (March, 1980), BS 2091, “Respirators for Protection Against Harmful Dusts and Gases” (1969), BS 4555, “High Efficiency Dust Respirators” (1969), EN 149 (April 2001)—the number of layers of filter material, filter material type, and available filtration area are important factors in filter element design. Investigators who design new filter element concepts attempt to create products that maximize the available filtration area by properly managing air flow across (and through) the filter media. Proper airflow management can prevent premature loading of the filter material. If the air-to-be-filtered is not uniformly distributed over the filter media during the filtering operation, the filtered particles may become unevenly collected by the filter, resulting in an early shortening of filter service life. Investigators also attempt to design respiratory products that are lightweight and evenly balanced on the wearer's head.
U.S. Pat. RE 35,062 to Brostrom et al. discloses a known lightweight filter element that uses a porous “baffle component” as a plenum to distribute air flow across the available filter element surface area. This filter element is adapted for attachment to a respirator facepiece and includes two layers of filter material that are separated by the baffle component. The '062 patent indicates that the baffle component can be made from woven or nonwoven webs, loose fibers, fiber batts, loose particulate material such as carbon particles, particulate material bonded together in a porous matrix, and combinations of such materials.
Examples of other filter elements are described in the following publications: EP0582007B1, U.S. 2003/0183233A1, U.S. Pat. No. 2,206,061, U.S. Pat. No. 2,220,374, U.S. Pat. No. 2,295,119, U.S. Pat. No. 2,320,770, U.S. Pat. No. 4,270,935, U.S. Pat. No. 4,501,272, U.S. Pat. No. 4,603,618, U.S. Pat. No. 4,886,058, U.S. Pat. No. 5,040,528, U.S. Pat. No. 5,156,738, U.S. Pat. No. 5,917,066, U.S. Pat. No. 6,680,028, and U.S. Pat. No. 6,761,162.